Dear Bob--I'm sure there are many full-time freelance photographers like me. I'm the sort who, during the film days, couldn't afford a Hasselblad; made do with the superb Mamiya TLR and equally superb Pentax 645, most of these systems picked up used. My film camera was not the Nikon F4 or F5, but FM2 or FE2 and many lenses--almost all purchased used. Nonetheless, I make a living (rather hand-to-mouth right now) and was able to put two children thru college with little debt on their part.In 2000, knowing that the digital age was upon us, I bought an Olympus E-10 to get started in a seemingly overwhelming new discipline. Good start, great lens, slow buffer. Professional SLRs were way out of reach for me then.But, in around 2004, a revolution happened and that was the 20D. At $1500 with lens, it was an affordable 8 megapixels. I soon acquired 10-22, 17-85 and 75-300mm lenses. I have made excellent prints of 36 inches and larger with that camera. I still appreciate Canon's overture. Although I wanted to stay with Nikon there was no similar Nikkor deal forthcoming.However, the camera died at about 18 months--in the middle of a job. Unlike you, I was not able to wait for the 40D. But at this time I could get a 30D at around $900, and did so. More robust, truly professional SLRs are frustratingly too expensive for me--and, of course, less than half of the lenses I now own will fit a full-frame Canon SLR.The 30D died after about nine months. The shutter would focus when pressed half way, but take as long as three seconds to finally fire after pressing down fully. This problem was not completely repaired on warranty. I sent it back, thinking I had the stated 6 months repair-warranty, only to find that it is only honored within the original one-year warranty. Basically the camera still hesitates to shoot.So, then on to the 40D. It seemed to be a much better camera, and it is most of the time. However, it exhibits mottling on the sensor which is only noticeable against an even background like the sky or a solid-color paper backdrop. This is extremely annoying, and the reason I write now. I recently had to reshoot with the 30D an assignment in which the sky had to be masked to bring up contrast, cut thru haze and make mountains stand out in the distance. The 40D made this mottling fairly glow!I have sent the 40D to Canon on warranty with specific images full-frame & enlarged to sky/backdrop on CD. Canon refused to acknowledge the problem, returning little 3x5s they had made and exclaiming they couldn't see the problem.And don't even get me into discussing 17-85mm lens' lack of edge sharpness, which is the reason I paid $1000 for the lens-creeping, color-fringing distorting 17-55mm, ad nauseum . . . . . .

You certainly seem to have had some bad luck. I'm surprised that Canon wouldn't repair your 30D for the second time under warranty. It can pay to call them and explain why you think that they should. Certainly if the same problem keeps cropping up despite "repair", I'd expect them to keep fixing it or replace the camera.

I've been lucky I guess. I've had a D30, 10D, 20D and 40D and none of them have had a problem.

I'm not sure what you mean by mottling with the 40D. Certainly you'll see noise at higher ISO settings and chroma noise can look a little like "mottling". Cranking up the contrast will certainly make it more visible. I can't compare the 30D and 40D because I don't have a 30D.

Sometimes you may have to do some editing to reduce the visibility of noise in uniform areas. Selective masking along with a mild smoothing or gaussian blur function can work well.

I honestly don't think Nikon, Pentax, Sony and Olympus are really very much different. I hear complaints from their users too. The technology isn't perfect I'm afraid.